Added support for inline collapsibles

fixes #64 
I changed the templates stacked and tabular to make the structure similar to fieldsets. So when "collapse" is applied to suit_classes the inline becomes collapsible. 

But to invoke collapse.js (being responsible for making fieldsets collapsible) at least one regular fieldset has to be collapsible. That is, because of some function in contrib.admin.helpers, that includes collapse.js only when necessary. 
To fix that I had to always include it in change_form. But then it is included twice when a regular fieldset is collapsible.
So I have created an own collapse.js called suit-collapse.js with the same code and included that instead. To prevent the old one from being invoked I have overridden collapse.js with an empty file.

Additionally I made some css changes (styled the add-row and removed the margin-top:15px of h2 inside .inline-group). I guess there is still some styling and cleanup required. That sounds like a lot changes but it is not that instrusive.

Edit: The PyCharm auto formatter makes form.less look like I changed everything. Sorry for that.